The term "multiple resistance" (MR) or
"multi-resistance" is used when a bacterial strain is resistant
to several different antimicrobials or antimicrobial classes. For instance,
multi-drug resistant tuberculosis is simultaneously resistant to a number of
antibiotics belonging to different chemical classes.

“Cross-resistant” bacteria are those that have developed
survival methods that are effective against different types of antimicrobial
molecules with similar mechanism(s) of action.

Bacteria can transfer bits of genetic material to other bacteria, and when
genetic information coding for several unrelated resistance mechanisms is
transferred in a single event and expressed in the new bacterial host it is
referred to as “co-resistance”.